This invention relates to films and fibers, and to materials that can serve as substitutes for plasticized polyvinyl chloride (PVC).
Plasticized PVC films and tapes are conventionally used for a wide variety of applications including graphic films, retroreflective sheeting, and auto paint masking. PVC has many advantages that have caused it to become a material of choice in such applications. For example, plasticized PVC films can readily be applied to many irregular surfaces. Thus a PVC-based graphic film or retroreflective sheet can be heated slightly above room temperature and stretched over rivets and into small indentations such as may be present on the substrates to which such graphic films or retroreflective sheets may be applied. Many materials that have been tried as substitutes for PVC have been found to undergo necking or other non-affine deformation when stretched, thus rendering such materials unsuitable for applications in which non-uniform distortion during stretching would be unacceptable.
Plasticizers are typically employed in PVC films in order to make the films more flexible and more stretchable. However, plasticizers can migrate to the substrate on which PVC films are adhered, leaving a residue or xe2x80x9cghostingxe2x80x9d when removed. In some cases the ghosting is not removable with solvent wipes. Thus, the exterior appearance of an automobile may be detrimentally affected when PVC films are used as the tape backing in auto paint masking tapes. Furthermore, PVC plasticizers can degrade the performance of adjacent adhesive layers, reducing the adherence of a tape to an automobile, or a graphic to a substrate. PVC plasticizers can also migrate into and thereby degrade the performance of retroreflective sheeting.
In addition, there is growing concern, particularly in European and Japanese markets, about the environmental impact of land filling or incinerating PVC materials. PVC has only limited recycling utility.
A variety of stiff, relatively high modulus packaging films (e.g., twist films for candy wrapping) have been made from isotactic (crystalline) polypropylene and hydrocarbon resins, including the films described in U.S. Pat. Nos. 3,278,646; 3,361,849; 3,666,836; 4,032,493; 4,289,831; 4,394,235; 5,091,237; 5,128,183; 5,212,009; 5,213,744; 5,246,659; 5,290,635; 5,451,455; 5,543,223; 5,560,948 and 5,777,055; and in European Patent Specification No. EP 0 681 914 B1. U.S. Pat. No. 5,085,943 also describes a twist film made from polypropylene and hydrocarbon resin, the film being said to have increased stiffness. PCT International Application Nos. WO 98/38041, WO 99/2331 and WO 99/51432 describe multilayer films having a core layer that contains isotactic propylene and various modifiers including atactic polypropylene. European Patent Specification No. EP 0 763 422 A1 refers to various multilayer films containing low-modulus polypropylene in an interior layer, and refers to but does not exemplify film layers containing a blend of low-modulus polypropylene and hydrocarbon resin.
Fibers made from isotactic polypropylene and hydrocarbon resins are described in, for example, U.S. Pat. Nos. 4,115,620 and 5,171,628, and in European Patent Application No. 0 399 792 A3.
Hot melt adhesives, sealants and other compositions containing, inter alia, atactic (amorphous) polypropylene and various hydrocarbon resins are described in many references, including U.S. Pat. Nos. 3,341,626; 3,983,206; 4,048,376; 4,081,415 and 4,279,659. U.S. Pat. No. 4,999,231 describes cast hot melt adhesive films for use on carpet backing, wherein the films contain, inter alia, atactic polypropylene, hydrocarbon resin and calcium carbonate filler. U.S. Pat. No. 4,692,370 describes a fibrous coating made from blown strands of a hot melt material made from, inter alia, atactic polypropylene and a polyterpene resin. U.S. Pat. Nos. 5,047,462; 5,248,719 and 5,472,764 describe coating compositions containing, inter alia, various atactic copolymers and hydrocarbon resin. European Patent Application No. 0 557 593 A2 describes packaging films containing, inter alia, a hydrocarbon resin and a wax. Atactic polypropylene is mentioned as one possible wax.
PVC replacement films are described in, for example, U.S. Pat. Nos. 5,112,674; 5,132,074 and 5,460,861.
The present invention provides, in one aspect, a blend comprising polyolefin and hydrocarbon resin, wherein the polyolefin is semicrystalline and has a suitable degree of crystallinity and molecular weight, or the polyolefin is amorphous and has sufficiently high molecular weight, and sufficient hydrocarbon resin is present in the blend, so that a film made from the blend is substantially vinyl-like and non-elastomeric. In other embodiments, films made from such a blend are also conformable, drapable or affinely deformable by hand.
In another aspect, the invention provides films and fibers made from the above-mentioned blend.
In another aspect, the invention provides multilayer films and fibers comprising a core of the above-mentioned blend and one or more additional layers made of a different material.
The invention provides, in yet another aspect, a vinyl-like non-elastomeric film comprising a blend of hydrocarbon resin together with semicrystalline or amorphous polyolefin, or a mixture thereof. In a preferred embodiment, the polyolefin comprises an ethylene or propylene copolymer, a mixed tacticity polypropylene, or a blend thereof.
The invention also provides a method for making a plasticized-PVC-like film comprising blending, extruding and optionally orienting a mixture comprising polyolefin and hydrocarbon resin, wherein the polyolefin is semicrystalline and has a suitable degree of crystallinity and molecular weight, or the polyolefin is amorphous and has sufficiently high molecular weight, and wherein sufficient hydrocarbon resin is present in the blend, so that a film made from the mixture is substantially vinyl-like and non-elastomeric. In other embodiments, the films are also conformable, drapable or affinely deformable by hand. In yet other embodiments, the films are oriented sufficiently so that the film has a deformation index (as defined below) that is less than about 1.1.
The invention provides films having vinyl-like features and behavior. The blends and method of the invention can be tailored to provide specific desired physical properties at room temperature (20xc2x0 C.) and at elevated temperatures, and can provide workable substitutes for existing plasticized PVC films and fibers. At present raw material pricing, the invention enables a desirable reduction in raw material cost compared to the use of many PVCs.